Cycle frames have formed the subject matter of numerous constructive propositions, from constituent elements of metal, plastics material, composite material, moulded in one piece or assembled by welding, adhesion or other modes of fit.
Whatever the embodiments, a cycle frame may be considered as always comprising an upper, generally substantially horizontal tube, a lower tube inclined downwardly from the upper tube, a rear fork extending from the lower end of the inclined tube and rear stays joining the ends of the fork to the upper tube.
As a general rule, a strut, called a "seat tube" is interposed between the lower tube and, substantially, the point of junction between the upper tube and the stays.
Such a triangulated structure presents a good resistance and makes it possible to fit, at the connection points, a steering pivot for the assembly of a front fork, a seat tube, a crankset casing and bearings for receiving the axle of a rear wheel.
In order to ensure maximum comfort, optimum output and good efficiency of the physical energy developed, it has been -observed for a long time that certain dimensional characteristics of the frame thus formed should correspond to the user's morphology.
For each individual, the size of the frame, the distance between the steering pivot and the seat tube, the setback of the seat tube with respect to the vertical passing through the crankset casing, must thus be taken into account. For technical reasons, it is also necessary to consider the clearance angle given to the steering pivot charged with retaining and allowing pivoting of the front fork.
In order to take into account all this data, two methods are employed for the construction of the frames.
The first is the so-called unit method which takes into account the user's morphological characteristics to determine the dimensional characteristics of the frame. It is certain that this method of construction is the most rational, but that it may be envisaged only in particular cases, as the manufacturing costs are prohibitive.
The second method consists in determining several ranges of manufacture, in each of which the dimensional characteristics are chosen, approximately, in order to constitute a compromise which is the least penalizing.
This method, which is less satisfactory, gives better results economically, as it allows the frames to be produced on a greater industrial scale, whatever the constituent materials employed.
However, in practice, this method has proved to lead most frequently to providing a user with a frame which gives greater dissatisfaction than economical advantages, due to the impossibility of suitably adjusting the different dimensional characteristics as a function of the user's real morphology.
It is an object of the present invention to overcome the drawbacks set forth hereinabove by proposing a novel cycle frame which may be made of any appropriate material, on an industrial scale, at an advantageous cost price and with a small number of predetermined ranges, from which the specific adjustments, as recalled hereinabove, may be made rapidly, simply, efficiently and inexpensively, producing a frame whose dimensional characteristics may easily be adapted to the user's requirements.
The invention aims more specifically, but not exclusively, at cycle frames made by moulding composite materials.
Another object of the invention is to propose a novel frame which, whilst responding to the objectives set forth therein above, in addition presents very good characteristics of mechanical strength, even resistance to torsion in its plane, so as to enable maximum output of the physical energy developed during pedalling to be obtained.